In recent years, an increase in cholesterol intake accompanying the diversification in our eating habits has become a serious social problem in connection with diseases. Namely, we frequently eat foods of a high cholesterol content these days. As a result, cholesterol contained in these foods elevates the blood cholesterol level, which is the major cause of, for example, arteriosclerosis.
To lower the cholesterol content in these foods, there have been reported some methods for decomposing cholesterol with the use of cholesterol oxidase.
Rice bran contains a number of components. For example, .gamma.-OZ, which is prepared by purifying these components, is a mixture of ferulates of various vegetable sterols and triterpene alcohol. For example, .gamma.-OZ consists of 14% of campesterol ferulate, 1% of stigmasterol ferulate, 4% of .beta.-sitosterol ferulate, 2% of cycloartanol ferulate, 35% of cycloartenol ferulate and 44% of 24-methylene cycloartanol ferulate.
As examples of the application of .gamma.-OZ to medical purposes, there has been reported that it has pharmacological effects of promoting growth, controlling diencephalic function, lowering serum cholesterol level, increasing amine-like compounds in amygdaloid nucleus and stimulating gonad, and clinical effects of treating menopausal disorders and autonomic imbalance.
Regarding the above-mentioned effect of .gamma.-OZ of lowering serum cholesterol level, its effects on catabolism/excretion of cholesterol in rat has been reported Geriatric Medicine, vol. 18, 519-524 (1980); Domyakukoka (arteriosclerosis), vol. 11 (2), 411-416 (1983)!.
In the field of food, .gamma.-OZ has been employed as an antioxidant. However, since .gamma.-OZ exhibits only a very weak antioxidant effect, it is scarcely used alone but mixed with tocopherol so as to enhance its effect.
Also, it is reported that organic acid esters of triterpene alcohol, namely, derivatives of the main constituent of .gamma.-OZ, are applicable to drugs for treating hyperlipemia (JP-A-61-243022 and JP-A-61-243099; the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Although these drugs aim at treating this disease by preventing an increase in serum cholesterol level or lowering the same, their function mechanisms have not been clarified in detail so far.
As discussed above, .gamma.-OZ or rice bran component derivatives have been studied and applied as drugs. However, no attempt has been made so far to clarify their function per se of directly binding to cholesterol to form a cholesterol complex and they have not been used as a food additive by taking advantage of this function.
Today, mayonnaise is a seasoning which is essentially needed in our westernized eating habits in Japan. In general, mayonnaises are produced by adding edible oils, vinegar, seasonings etc. to egg white and yolk to form an oil-in-water emulsion.
With the recent tendency toward health foods such as low-cholesterol or low-salt foods and a variety of tastes, there have been proposed mayonnaises free from cholesterol or containing cholesterol in a reduced amount which are produced by using no or little egg yolk. For example, JP-A-50-64466 has proposed an egg yolk-free mayonnaise produced by using starch paste and egg white, while JP-A-63-275 has proposed a mayonnaise produced by using soybean flour. Further, JP-A-60-43347 has proposed a process for producing a mayonnaise having a function of lowering blood cholesterol level or suppressing an increase of the blood cholesterol level, in which monolinolein is added to an edible oil to be used.
Not only chemical seasonings and spices but also egg components, in particular, egg yolk largely contribute to the flavor of mayonnaise. In addition, egg yolk plays an important role in the shape retention when mayonnaise is used in salad dressing placed on salad.
Namely, since mayonnaise has a high acidity due to vinegar which is used in a large amount, a stable emulsion of mayonnaise can hardly be achieved by using common edible emulsifiers and it is highly important to use the emulsifying power of egg yolk.
Thus, it is considered that the use of egg yolk is an essential requirement in the production of mayonnaise.
The conventional mayonnaises being free from egg yolk or containing egg yolk in a reduced amount have no or only deteriorated body taste of egg yolk. Further, they are not satisfactory in shape retention properties as a mayonnaise to be used as a seasoning.
On the other hand, the method of adding monolinolein to fat and oil suffers from a problem that monolinolein is hardly available. In addition, only an unsatisfactory effect of lowering blood cholesterol level is achieved by this method.